Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
For example, in a flat plate type solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-172594, a separator 1a as shown in FIG. 17 is provided, and a plurality of unit cells (not shown) and separators 1a are stacked alternately. Gas supply holes 2aa, 3aa, and gas discharge holes 2ab, 3ab extend through four corners of the separator 1a in the stacking direction, and a plurality of gas flow grooves 4aa and ridges 4ab in a plurality of rows are arranged alternately along the surface of the separator 1a. 
The gas flow grooves 4aa are connected to the gas supply hole 2aa and the gas discharge hole 2ab through triangular recesses 5aa, 5ab. A throttle section 6a and blocks 7a are provided in a gas inlet section of the triangular recess 5aa, near the gas supply hole 2aa, as means for limiting the flow rate of the gas. The throttle section 6a and the blocks 7a function to increase the pressure loss of the gas flowing from the gas supply hole 2aa to the gas inlet section for equal distribution of the gas.
Further, at opposite ends of the gas flow grooves 4aa, a shallow gas flow inlet section 8aa and a shallow gas flow outlet section 8ab are provided to cause a pressure loss in the gas flow.
Further, in a solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2005-085520, as shown in FIG. 18, the fuel cell is formed by stacking power generation cells 1b, fuel electrode current collectors 2b, air electrode current collectors 3b, and separators 4b. The power generation cell 1b includes a fuel electrode layer, and an air electrode layer, and a solid electrolyte layer interposed between the fuel electrode layer and the air electrode layer. The fuel electrode current collector 2b is provided outside the fuel electrode layer, and the air electrode current collector 3b is provided outside the air electrode layer. The separators 4b are provided outside the current collectors 2b, 3b. Though not shown, a ring shaped metal cover covers the outer circumferential portion of a circular porous metal body making up the current collector 2b, and a large number of gas outlets are provided over the entire circumferential side portion of the cover at predetermined intervals.
In the structure, the fuel gas diffused in the porous metal body is prevented from being emitted from the entire outer circumferential portion of the porous metal body. According to the disclosure, the amount of the fuel gas which is not used in the power generation and discharged from the outer circumferential portion is suppressed, and the fuel gas is thus supplied to the power generation cell 1b efficiently.
Further, in a flat stack fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-120589, as shown in FIG. 19, a separator 1c stacked on a power generation cell is provided. The separator 1c is formed by connecting left and right manifold parts 2c and a part 3c disposed at the center where the power generation cell is provided, by joint parts 4c. The joint parts 4c have elasticity.
The manifold parts 2c have gas holes 5c, 6c. One gas hole 5c is connected to a fuel gas channel 7c, and the other gas hole 6c is connected to an oxygen-containing gas channel 8c. The fuel gas channel 7c and the oxygen-containing gas channel 8c extend in a spiral pattern into the part 3c, and are opened to a fuel electrode current collector and an air electrode current collector (not shown), respectively, at positions near the center of the part 3c. 